The subject invention concerns a method of manufacturing filter units comprising a plurality of filter tubes of synthetic fibres and natural fibres, and a machine designed to perform the method.
Prior-art multi-tube filters suffer from several drawbacks as regard the manufacture and the assembly as well as the function of the filters.
Hitherto, lengthwise stitched seams have been used to produce the filter, which is a very time-consuming method. It takes several hours to sew in the conventional manner a filter unit having a cross-section of 1 by 1 meter and a tube length of 1 meter. In the manufacture, only one tube row may be produced at a time, lengthwise seams in two interconnected parts of the material delimiting separate filter tubes. The rows of filter tubes are then stitched together at one end to form a filter unit.
A filter produced in this way lacks inherent stability and in order to operate as an efficient filter it must be stayed by means of special supporting, profiled rods which are inserted into each individual tube to keep it distended. Naturally, the application of special supporting profiled rods into each tube is a time-consuming task. In addition, it increases the total weight of the filter unit. On account of the resulting considerable weight of the filter unit, the latter becomes difficult to handle during assembly, and in addition the filter material which is to support both its own weight and the supporting profiles, is exposed to considerable stress. Because in operation the filter tubes move somewhat relative to the supporting profiled rods on account of the streams of gas passing through them, the rods cause a certain amount of wear on the filter material. A further disadvantage inherent in these prior-art multi-tube filters is that the support profiles, one inside each tube, occupy a considerable portion of the filtering area of the filter unit, thus considerably reducing the capacity of the filter.
Finally should be pointed out that the collapsing pressure, i.e. the maximum pressure that the filter is capable of withstanding, is comparatively low on account of the stresses exerted on the filter unit on account of its heavy weight. The same is true as concerns the cleaning pressure, i.e. the maximum allowable flow of air in the reverse flow direction through the filter to clean the latter.
The above-mentioned disadvantages are completely eliminated in the filter produced in accordance with the method of the subject invention.